Peterson & Peterson

Categories: MemoryPetPsychology

The experiment will be largely based upon that of Brown (1958) and Peterson & Peterson (1959), which used the technique of blocking rehearsal within the short term memory (STM) by tasks such as counting backwards.

The two groups of researchers independently investigated the capacity of the STM using a technique which involved presenting subjects with trigrams, which are three letter syllables which make no sense, (for example HTK) for a short time and testing recall after a specific retention interval. Results showed that items are rapidly forgotten when the process of rehearsal is prevented by a task such as counting backwards. It was concluded by the two groups of researchers that information stayed in the STM, without rehearsal, for a maximum of 18 seconds, and this theory still remains. These results were paramount to proving the existence of the STM.

A pilot study was carried out using two group of ten males, aged 16-18, using opportunity sampling within the school common room, and asked each member to commit as many trigrams as possible to memory for one minute, from a list of twenty compiled previously.

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I then allowed ten out of the twenty participants a 'rehearsal time' of 20 seconds, which involved the member on his own, with no other contact with any other participants, going over the trigrams in his head. I then asked each participant to recall as many trigrams as possible. The participants were selected one at a time, whereby once one had finished reciting his trigrams, another was selected and asked to take part in the experiment.

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The second group of participants were approached in the same way, but after being allowed one minute to commit the trigrams to the STM, they were asked to hand back the sheet, and count down in numbers of three from 672, a randomly selected 'high number', again for the period of 20 seconds, and they were then asked to recite as many trigrams as possible within the time allocated. The counting down from a high number was an example of interference, and was necessary to the experiment.

The results clearly showed that the participants who did not experience any interference were able to recall many more trigrams that those who had to count backwards from a high number. Although these results supported the original experiment, they were far from ideal. I would have liked to have used a wider pool of participants, and this is what I intend to do in the forthcoming experiment. The ecological validity of this experiment should also be questioned, but this will take place later on in the experiment, as it should be applied to the findings of this experiment too.


This experiment is designed to test the Rehearsal Loop, first put forward by Atkinson & Shiffrin (1968), which is key to cognitive psychology with regards to information processing. The diagram is very basic, and shows that information enters the sensory store, then is transferred to the STM. If the information is rehearsed, it will move into the LTM. If it not rehearsed, the information will be lost before it reaches the LTM. During this experiment I will be using the Brown-Peterson technique, a technique established in order to test the rehearsal loop developed by Atkinson & Shiffrin, a well known technique which involves 'blocking' the information from entering the LTM to test the existence of the Rehearsal Loop.

One primary reason for my participation in this particular study is the general interest I have towards this experiment. I feel I would enjoy recreating the study, and although on a much smaller scale, applying the results to today's society, and seeing how much the validity still applies after just under 50 years. It has been proven that information can stay in the STM for little over 18 seconds, ad certainly not a great deal more than that. I hope to prove that in my results.

Updated: May 20, 2021
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Peterson & Peterson. (2020, Jun 02). Retrieved from

Peterson & Peterson essay
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